Few bands have a reputation for making music as consistently honest, organic and daring as Gov't Mule. Now the enduring group fronted by visionary singer-guitarist Warren Haynes returns with their first album in four years - their Blue Note Records debut Shout!, a breath-taking, exploratory double-disc set to be released on September 24.

"This album puts a spotlight on the songs and the way that we interpret them, which hinges on the unique chemistry we've developed as a band," explains Haynes, who along with Mule co-founder and drummer Matt Abts, multi-instrumentalist Danny Louis and bassist Jorgen Carlsson charted Shout!'s adventurous contours.

"No one's done this before, which is exciting," says Haynes, "but it's even more exciting actually listening to these artists sing our songs. Their performances bring new ideas, energy and sometimes even different meanings to every number."

Plus Shout! offers some of the most extraordinary playing in Gov't Mule's rich, sonically colorful history. And the album's incredible scope ranges from the suite-like epic "Bring On The Music" to the snarling punk rock anthem "Funny Little Tragedy" to the soul-reggae testifier "Scared To Live."

The inventive and incendiary musical performances throughout both discs spring from the jazz-like philosophy and creative language the Mule's members have developed together. They're the rare rock ‘n' roll group with an improvisational heartbeat, which allows all four musicians to expand on the songs' themes in non-formulaic ways. That quality distinguishes the finest jazz, blues and rock recordings of the '50s and '60s, but is largely absent in modern music.

On Shout! it's audible from the ground up - starting with the Technicolor propulsion of the Abts-Carlsson rhythm section. Their flexible interplay in the studio and on stage, where both musicians amp up their already aggressive, freewheeling approach to providing the sonic foundation of the band, is essential to Gov't Mule's reputation as a living, breathing ensemble. Drummer Abts has the courage and the chops to extrapolate with the other band members, pushing, pulling and accenting his rhythms as each performance evolves. And while Carlsson's bass always keeps its essential snarl, he's among the few players in modern rock that varies his tone and approach to best serve each song.

Although Louis' primary role in Gov't Mule is keyboardist, his guitar playing has expanded to the point where he often plays the instrument for a third of the band's live sets. On Shout! he steps even further into the role of Haynes' six-string foil, with their contrasting styles frequently adding yet another dimension to the album.

Several numbers were cut with Haynes and Louis simultaneously on guitar, including the romantic "Captured," which shares a shimmering ebb and flow with classic Neil Young & Crazy Horse.

Louis even takes the brash, ringing fret board solo on the Clash-inspired "Funny Little Tragedy." And he steps up his contributions as a background singer, adding vocal support to five songs.

And Haynes, of course, remains one of the most formidable guitarists and vocalists of the modern era, effortlessly cross-pollinating genres and unfurling solos that broil with passion in his distinctive, signature style.

No wonder fans of the Grammy nominated band have come to expect nothing less than the virtuosity, intelligence and breadth that propels Shout!.

Here's how Blue Note Records president Don Was, who's also a Grammy winning producer and performer, sums up Gov't Mule's place in contemporary music: "The Mule holds a unique and lofty berth. They have roots that run real deep - drawing from the entire history of rock ‘n' roll going all the way back to Robert Johnson and the Delta. Yet, despite their mastery of past idioms, they have managed to rearrange those elements into a whole new thing. So while the music they make is quite contemporary, I dare say they have deeper roots than other bands that are creating new music.

"According to the Blue Note manifesto written by our founder Alfred Lion back in 1939, our label is dedicated to the recording of ‘authentic music.' I don't know how much more authentic you can be than Gov't Mule! It's an honor to release their records on the Blue Note label. On this new album, they've elevated their songwriting, playing and production values to a whole new plateau. It's gonna blow people's minds!"

Add the word "again," because Gov't Mule have been blowing minds since their eponymous 1994 debut. That album found the band boldly transfusing new blood into old-school psychedelic blues-rock at a time when the genre was largely ignored. Gov't Mule's stylistic grasp has grown inexhaustibly since.

Fighting the trend in a declining music industry, the band's fan base, too, has steadily expanded over the course of 15 studio and live releases and thousands of performances - at first in small clubs and theaters, then at halls and major international festivals.

Today, Gov't Mule have become a human encyclopedia of great American music even while adding to that cannon. And through it all Haynes has served as not only the group's captain, but as a beacon of creativity and excellence that inspires fans and fellow musicians.

Parallel to his nearly two decades in the Mule, Haynes has been the six-string mainstay and a vocalist for the Allman Brothers Band and the Dead, and performed or recorded with a diverse array of other artists. In 2011 he made his second in-studio solo album, the aptly titled Man In Motion, which paid tribute to his blues roots and found Haynes experimenting with different guitar tones and effects not traditionally associated with Gov't Mule.

Shout! came to life in a Connecticut studio where the band initially regrouped to reignite their collective flame, and ended up cutting the bulk of the album, with Haynes, his bandmates and longtime Mule collaborator Gordie Johnson producing various cuts. Three songs - the reggae-based "World Boss," the psychedelic dreamscape "Whisper In Your Soul" and the blues-rocker "Done Got Wise" - were recorded at Jorgen Carlsson's Rogers Boat Studios in California, with Carlsson and studio co-owner Steve Holroyd engineering.

Paying tribute to the band's musical heroes became part of Shout!'s creative game plan. Haynes explains that the brawny "Bring On the Music" was written to celebrate the 40th anniversary of the break-up of the classic British blues-rock band Free.

Every note of "Bring On The Music" evokes Free's memorable style - especially Haynes' channeling of the band's fiery Les Paul guitar playing of the group's leader Paul Kossoff.

Another sinewy number, "How Could You Stoop So Low," is a nod to the 40th anniversary of the release of Sly & the Family Stone's influential album Fresh and was co-written by Haynes and Louis, whose rhythm guitar riff is the song's spine. The four-piece Mule was able to recreate Sly's nine-piece sound with the addition of backing singers Alecia Chakour and Nigel Hall from Haynes' solo-project band, and Louis' heavily funky keyboard lines.

Dr. John's grizzly, incantatory turn on the alternate version of the tune was the first guest vocal recorded, although the idea of assembling a cast of great singers to color the songs differently was indirectly inspired by Haynes' friend Elvis Costello. Early in the project Haynes wrote the snarling "Funny Little Tragedy," which reminded him of Costello's early music, and called Costello to ask him about the vocal mics used for his first albums. After the conversation, Haynes started thinking about how the song would sound if Costello sang it. As a result, he couldn't get Costello's voice out of his head and began thinking about pairing other vocalists with the set's other songs.

So Haynes made a list of Shout!'s titles and his top choices for singers, and their responses were overwhelming - a tribute to Haynes' and Gov't Mule's standing among their peers.

"Everyone in the band has such a wide variety of musical points of reference that a song can start in any style - from rock to blues to funk to R&B to reggae - and end up going to a completely different place.

"On Shout! every performance of each song stands on its own, but always sounds like us," he adds. "Even if it's a part of us that most people have never heard before."

In reflection, Haynes offers that Gov't Mule's journey has been full of surprises. "There's no way I could have anticipated the way we'd grow when we started," Haynes remarks. "Everyone in Gov't Mule brings their own personality to the music, and we're always looking for opportunities to expand and excite ourselves. Shout! is proof of that, as well as an album I could never have predicted we'd make even five years ago."

In 2000, when founding bassist Allen Woody passed away, Haynes and Abts discussed the possibility of putting Gov't Mule out to pasture. Instead the band went on to become part of the tradition they had always intended to honor.

"That," says Haynes, "is something we could only have dreamed to achieve and never expected in a million years."